1. Field of the Invention
This invention relates to an ink jet recording head and a base plate therefor.
2. Related Background Art
The ink jet recording method is a recording method whereby ink (recording liquid) is discharged from a discharge port provided in a recording head and the discharged ink is caused to adhere to a recording medium such as paper to thereby accomplish recording. Advantages of such a method include advantages such as very little noise being produced, the capability of high-speed recording and no necessity of using paper of special construction for recording, and recording heads of various types have heretofore been developed.
Above all, a recording head of the type in which heat energy is caused to act on ink to discharge the ink from a discharge port has advantages such as good responsiveness to recording signals and the ease with which a number of discharge ports are disposed at high density.
As a recording head of such type which utilizes heat energy as ink discharging energy, there is known a recording head of a construction in which electro-thermal converting elements having a heat generating resistance member layer and electrodes are arranged on a substrate, the converting elements having as required a protective film provided above the portion thereof which contacts liquid, and a top plate formed with liquid paths and a liquid chamber joined thereto.
The ink discharging energy in a recording head utilizing this system is generally imparted by an electro-thermal converting element having a pair of electrodes and a heat generating resistance member located between the electrodes. That is, when an electric current is applied to the electrodes to cause the heat generating resistance member to generate heat, the ink in the liquid path in contact with or near the heat generating resistance element is momentarily heated and bubbles are created therein. Ink droplets are discharged from the discharge port by the change in volume resulting from the momentary expansion and contraction of volume caused by the creation of the bubbles.
In the recording head using the electro-thermal converting element as described above, other portions than the heat generating member are generally protected by an organic resin film to prevent the occurrence of leakage or short circuit of the electric current through the ink. In such case, the organic film has not been provided on the heat generating member of the heat generating portion because it adversely affects the heat conduction, or because of its heat resisting property. Also, because of its heat resisting property or the like, it has been necessary that the organic film be formed separately from the heat generating member of the heat generating portion. However, the separation of the organic film from the heat generating member of the heat generating portion has sometimes led to the problem that the electrodes connected to the heat generating member can no longer be protected and the reliability is reduced. As a countermeasure for this, it has been practiced to provide an intermediate area between the heat generating member and the electrodes and form in this intermediate area the end of the organic protective film which is adjacent to the heat generating member.
As such method, there is a method of widening the pattern width of the heat generating resistance member as disclosed, for example, in Japanese Laid-Open patent application No. 033471/1983, but according to this method, in some cases, a so-called heat spot of high current density has been produced at the corner in which the pattern of the heat generating member is thinner, thereby adversely affecting the creation of bubbles. Also, in German Pat. No. 3443560, there is proposed a construction in which the thickness of the portions of the electrodes which are near the heat generating member is made small, but a method of making the thickness of a part small by a single electrode layer is difficult to control, and a method of using two layers and selectively etching the two layers has presupposed that the heat generating member and the two kinds of electrodes can be selectively etched, and has suffered from the problem that the limitations in the usable materials and the etching liquid or the etching method are severe.
That is, there have been problems still left to be solved in search of a more ideal electro-thermal converting element in which the protection of the electro-thermal converting element and the prevention of leakage or short circuit are accomplished more perfectly and which does not adversely affect the creation of bubbles.